Tcl

Require Specific FTPS Server Certificate Fields

Demonstrates the Chilkat Ftp2.SetSslCertRequirement method, which adds a required match against the FTP server certificate. The first argument selects the certificate field (such as SubjectCN or IssuerCN) and the second is the required value. It is a void method; a non-matching certificate causes the connection to fail.

Background: Standard TLS validation confirms a certificate is trusted and valid for the hostname, but it does not guarantee you reached the specific server you expect — a form of pinning closes that gap. Requiring a certificate field to match a known value rejects any certificate that does not, defending against a mis-issued or substituted certificate even if it would otherwise pass validation. Multiple requirements can be added, and all must be satisfied.

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Tcl


load ./chilkat.dll

set success 0

#  Demonstrates the Ftp2.SetSslCertRequirement method, which adds a required match against the FTP
#  server certificate.  The 1st argument selects the certificate field and the 2nd is the required
#  value.  It is a void method.

set ftp [new_CkFtp2]

CkFtp2_put_Hostname $ftp "ftp.example.com"
CkFtp2_put_Username $ftp "myFtpLogin"

#  Normally you would not hard-code the password in source.  You should instead obtain it
#  from an interactive prompt, environment variable, or a secrets vault.
CkFtp2_put_Password $ftp "myPassword"

#  Use explicit FTPS (AUTH TLS) on the standard FTP port.
CkFtp2_put_AuthTls $ftp 1

#  Require that the server certificate's subject common name matches an expected value.  If the
#  presented certificate does not match, the TLS connection fails.  Supported fields include
#  SubjectDN, SubjectCN, IssuerDN, IssuerCN, and others.
CkFtp2_SetSslCertRequirement $ftp "SubjectCN" "ftp.example.com"

set success [CkFtp2_Connect $ftp]
if {$success == 0} then {
    puts [CkFtp2_lastErrorText $ftp]
    delete_CkFtp2 $ftp
    exit
}

puts "Connected; server certificate met the requirement."

set success [CkFtp2_Disconnect $ftp]
if {$success == 0} then {
    puts [CkFtp2_lastErrorText $ftp]
    delete_CkFtp2 $ftp
    exit
}


delete_CkFtp2 $ftp